This invention relates to electromagnetic relays and contactors, and is more specifically related to the structure of an electromagnetic or electromechanical relay of the type that has a winding or coil that is energized to move an armature such that a load current may be applied to a load device. Relays and contactors may be considered as devices in which the appearance of a pilot current or voltage causes the opening or closing of a controlled switching device to apply or discontinue application of load current. The invention is particularly concerned with a the structure of the magnetic pole piece of the magnetic core of the winding, and the corresponding pole piece of the movable armature, structured in a way that manages the magnetic flux between core and armature as the armature closes so as to avoid noise, chatter, and wear, and to permit the relay to operate at smaller values of current for a given coil.
Electromagnetic or electromechanical relays or contactors are devices in which current that flows through an actuator coil closes or opens a pair (or multiple pairs) of electrical contacts. This may occur in a number of well-known ways, but usually a ferromagnetic armature is magnetically deflected towards the core of the coil to make (or break) the controlled circuit.
Electromagnetic or electromechanical relays are commonly used to control the application of power to a load, for example, to control the application power to a blower or fan in a ventilation, heating, or air conditioning system. These devices are inexpensive and in general have good reliability over a reasonable life span. However, due to the fact that the magnetic flux has to move across a gap that diminishes as the armature closes, the armature of the relay experiences a maximum force and acceleration at closure, which can result in a loud slapping noise, and can also produce bounce and chatter at the normally-open (NO) contact. The bounce or chatter may also produce RF switching noise, which may disturb electronic devices located near the relay.
A conventional relay is formed of a relay coil mounted on a yoke or frame of a ferromagnetic material. A core, i.e., a post formed of iron on which the coil is mounted, is affixed to the yoke, and a movable armature, also formed of ferromagnetic material, is mounted at an armature bearing, i.e., a hinge, to the yoke. The armature extends across the axis of the core of the coil, and a spring biases the armature away from the core so as to form a magnetic gap between the tip or magnetic pole face of the core and a facing surface on the armature. A conductive arm is supported on the armature and carries one or more movable contact members. In a typical relay, a normally-closed or NC movable contact is biased by the spring against a fixed normally-closed contact, and a normally-open or NO movable contact is biased by the spring away from a fixed normally-open contact.
In the conventional relay, the core pole face is a generally flat surface, and the facing portion of the armature is also a flat surface.
In order to actuate the relay, i.e., to close the normally-open contacts, current is supplied to the coil at sufficient amperage so that the magnetic force between the core pole face and the armature will overcome the spring force, and move the armature to a closed position against the core. At the initial open position, the gap is relatively large, but as the armature moves, the gap becomes smaller and smaller. For any given number of ampere-turns in the coil, the magnetic force felt by the armature will be in proportion to the inverse cube of the gap distance or separation between the armature and the core pole face. Consequently, a relatively large current is initially required to overcome the spring force and start the closure motion of the relay armature. Then at that same current, the force on the armature increases sharply as the gap distance diminishes. This results in a large acceleration just as the armature reaches the pole face of the core. The sudden collision of the armature with the core can cause the armature to bounce off, and can also cause the normally-open contacts to open and close intermittently, creating chatter and also producing arcing and RF switching noise. In addition, the relay closure can be audible, and present unpleasant clicking noises to persons present in the vicinity.
To date, no one has come up with any effective way to limit or control the magnetic forces involved with relay actuation, and no one has effectively reduced relay noise, chatter, or RF switching noise. It has been previously proposed, e.g., in Kozai et al. U.S. Pat. No. 7,932,795 and in Copper et al. U.S. Pat. No. 6,798,322 to place a cushion, pad or bump between the core pole face and the armature as a way of cushioning the closure of the armature so as to avoid audible or acoustic relay noise. However, these arrangements add to the complexity of the coil, do not level out the magnetic force on the armature, and have limited success at reducing chatter and electrical switching noise.